Field Of The Invention
The present invention relates to a system for generating a uniform field of energized gas and, more particularly, to a system having segmented electrodes for use in plasma processing.
In the manufacture of many electronic components, such as integrated circuits and semiconductor devices, there is a need to deposit material onto, and etch material from, substrates. In particular, metal such as copper is often deposited and material such as epoxy glass is often removed.
In the field of plasma deposition, an atom may be displaced from the surface of the target connected to a cathode by a process called sputtering or sputter deposition. In this process, the target may be constructed of copper or of another material. The cathode to which the target is attached is subjected to a high voltage in an inert atmosphere such as argon. The inert gas is ionized, forming a plasma from which positive ions escape to bombard the exposed surface of the target and to dislodge by momentum transfer the atoms or clusters of atoms of the target material. It is this dislodging of the target atoms that is known as sputtering. By repeating this process, a number of these primarily neutral atoms move through the space in front of the target, in a relatively high vacuum, until they strike and condense on the surface of a receiver, known as a sample, substrate or workpiece, which is generally in close proximity to the target. A coating of atomic or molecular layers of target material can thus be built up on the substrate. The coating, which is generally less than 10 .mu.m, is generally sufficient for the metallization of integrated circuits.
The most commonly used plasma reactors have one or more targets oriented such that the surface of the target is parallel to the surface of the sample on which atoms are to be deposited. Atoms emitted from the target tend to be emitted in a non-uniform distribution. In particular, atoms around the edges of the target are not emitted at the same rate as atoms in the center of the target. Accordingly, the deposition of material on the substrate proximate the target is not uniform. Atoms that are ejected from the target perpendicularly and received at the sample surface perpendicularly provide optimum atom deposition thereof. A greater amount of material may be built up in the center of the substrate than at its edges.
Similarly, in etching processes, it has been found that material is etched to a greater extent along the periphery of a substrate than in the interior portions thereof. Substrates used to make printed circuit boards and cards, because they are large, are especially susceptible to non-uniformity of a plasma field, resulting in non-uniform etching, non-uniform deposition and/or non-uniform cleaning of thru holes or viaduct holes (commonly called vias). Vias are paths for electrical interconnections between a first-level conductive pattern and a second- or higher-level conductive pattern. Cleaning of thru holes is referred to as desmearing. In the etching process, for example, a more intense plasma field along the periphery of a workpiece results in a higher etching rate for that portion of the workpiece, whereas a relatively sparse plasma density in the center of the workpiece results in a predictably low etch rate for those sections. It has been found that non-uniformity of an electric field in proximity to a printed circuit board results in non-uniform plasma treatment thereof.
Decreasing the surface area of an electrode results in a more uniform electric field and corresponding plasma field around it. Unfortunately, for larger workpieces such as printed circuit boards and relatively large semiconductor devices, a small electrode is not economically feasible. A series of smaller electrodes, or a segmented electrode, however, in accordance with the present invention can solve the problem of non-uniform plasma field.
U.S. Pat. Nos. 4,361,441 and 4,394,162 issued to Tylko disclose a plasma reactor having spaced stationary electrode structures of which at least one is annular. Between the electrodes an arc is established by a power supply. The arc is pulsated and caused to orbit or circulate around the annular electrode structure to form a conical plasma zone between the electrodes while particulate solids are introduced to the plasma zone. Such apparatus is a possible alternative to industrial processes such as the manufacture of steel, ferro-alloys and cermets. The use of a conical plasma zone, however, is not especially useful for plasma processing of electronic components such as generally planar printed circuit boards and semiconductor devices.
U.S. Pat. No. 4,282,077 issued to Reavill discloses a generally planar electrode plasma reaction chamber, each of a plurality of electrodes being individually connected to a radio frequency (rf) power generator. The electrodes are arranged for defining separate part cells with means for individually and separately adjusting each of the cells.
U.S. co-pending patent application Ser. No. 894,240, filed Aug. 4, 1986 for "Side Source Center Sink Plasma Reactor" assigned to the present assignee, teaches the use of a plurality of planar electrodes in a continuous plasma etching system in which the plasma reactor chamber has provision for continuously introducing a gas and for forcing the gas through one or more thru holes in the substrates in order to remove material therefrom.
It would be advantageous to provide a plasma reactor system for generating uniform plasma fields.
It would further be advantageous to provide a system having two or more independently controlled electrodes for creating a uniform plasma field.
It would further be advantageous to provide a plasma system in which two or more electrodes were movable with respect to a substrate so that the plasma field created by the electrodes could be adjusted and controlled with specificity.
It would further be advantageous to provide a plasma system for uniformly desmearing or etching semiconductor devices.
It would further be advantageous to etch material from relatively large substrates uniformly.
It would further be advantageous to provide a system for depositing material onto a substrate in a uniform manner.